Measuring magnetic properties of materials and apparatus therefor.



W. ROGOWSKI. MEASURING MAGNETIC PROPERTIES OF MATERIALS AND APPARATUS THEREFOR. APPLICATION FILED FUGAS. 1913.

1,204,489, Patented Nov. H, 1916.

UNITED sTATES -PATENT OFFICE.

WALTER. BOGOWSKI, OF BEBLIN-CHARLOTTENBURG, GERMANY, ASSIGNOR TO SIEMENS &; HAIJSKE A. G., OF BERLIN, GERMANY, A CORPORATION OF GERMANY.

MEASURING MAGNETIC IPROPERTIES OF MATERIALS AND APPARATUS THEREFOR.

Specification of Letters Patent.

Patented Nov. 14, 1916.

Application filed August 5, 1913. Serial No. 783,181.

To all whom it may concern:

Be it known that I, WALTER Roeowsxl, a citizen of the German Empire, and resldent of Berlin-Charlottenburg, Germany, have invented certain new and useful Improvements in Measuring Magnetic PI'OPQIUBS. of Materials and Apparatus Therefor, of whlch the following is a specification.

My invention relates to a novel method of measuring magnetic qualit es of materials, for instance for detennining-the ampereturns necessary for magnetizing any magnetizable part of electric machines, such as yokes teeth magnet bodies armatures and the like. Also for carrying my invention into eifect I have devised a practical instrument for measuring the, magnetic flow, or more precisely stated, the magnetic tension existing between two points of the magnetic circuit. More theoretically expressed, the

quantity to be measured by my present invention may be stated as being the line integral of the magnetic strength. It may further be remarked that this quantity may be of interest for other purposes.

The present art of measurlng magnetic tensions is limited to measuring methods for the magnetic tension in closed magnetlc circuits, that is to say the line integral of the magnetic field strength developed in a closed magnetic circuit. By my present invention, now, I am enabled to determine the drop of magnetic fiow existing between two points of the magnetic circuit which will immediately be a measure for the magnetic tension existing between the said two points. In order to give a clear understanding of the method and apparatus of my present invention it will be necessary to briefly set forth the theory of the measuring method, which I aim to give in the following, without, however, intending to base my invention upon the correctness of this theory. In electrical circuits it is of great importance to measure the potential drop between the several points of the electrical circuit in addition to the value of the total driving -E. M. F. Likewise it is of particular importance in addition to measuring the magneto motive force which is given by the number of exciting ampere turns, to be able to measure in magnetic circuits the so-called magnetic tension existing upon any deslred path between any two points of a magnetic circuit. The magnetic tension between two points land 2 of a magnetic field, as well known, is determined by the line integral 55 d? over the magnetic field strength 1 along a line which may be arbitrarily drawn between these two points. In this formula 8 designates the length of the'path which is measured on the axis of the coil. According to this invention, now, I have devised an instrument which so far has been wantlng among the measuring instruments, vlz. an instrument for measuring these magnetic tensions. The operation of my present invention is based upon the following consideration: If .a coil be brought in a variable magnetic field an E. M. F. will be set up in said coil. If the flow of induction be designated with I the surface surrounded by a turn by F, and the perpendicular to this surface with s,-then will be obtained the following relation wherein 58, is the normal component of the magnetic induction. If a coil be made of constant cross-section and evenly spaced turns throughout, with such coil the magnetic tension between any two points may be measured upon any desired path. If- F be the cross-section of the coil and N the number of turns per length unit then the total magnetic fiow will be:

In this formula K is a constant, 23 the induction, 3;) the magnetic field strength and m the length measured upon the axis of the coil.

' I E. M. F. (partial): -'NdS Z Accordingly the E. M. F. set up in the The integral f @dx now, is identotal coil will be given bythe following equation:

2 E. M. F. (total)= -fN ds..

From this equation it follows that if N be the number of turns per length unit and if the cross-section F of the coil be constant all along its length, if furthermore the surface F be invariable with the time, the induced E. M. F. will also be expressed by the following relation:

From thi it follows that f,u$:) d8= INEFJL -fe.ds= fEdt.

The time integral of the induced E. M. F. therefore under the stated assumption will be an immediate measure of the magnetic tension. p

My new method of measuring the magnetic tension existing between any points of any desired oath consists therein that the coil in which the number of windings per length unit and the cross-section of the coil is constant at every place, is brought with both free ends at places of the magnetic field between which the magnetic tension shall be measured.

Provided that the magnet to be tested is excited with direct current, for instance, a ballistic galvanometer is placed at the ends of the coil. If the exciting current be re versed then in will be changed into and by the galvanometer a time integral of the F. will be indicated which may be expressed by the following formula:

From this formula the following relation tested be excited by alternating current, the

coil may advantageously be connected with an oscll'lograph. This oscillograph will record the course of the E. M. F. E induced in the coil as a function of the time and the value fEdt may be obtained from the oscillograph by integration. The apparatus of carrying out the above set forth measurements according to my invention will be more fully understood by reference to the accompanying drawing, of which 1 Figures 1 and 2 show in a longitudinal and'in a transverse section, respectively, one

form of carrying my invention into effect and of which Fig. 3 shows by the way of example in a diagrammatic V16W the mode of application of my present tension measuring instrument.

Referring now more particularly to the drawing; upon the core is, which may for instance be made of rubber orother flexible material in the form of a fiat band of elliptical cross-section, a winding 'w is provided, said winding having a plurality of turns and being arran ed in one or morelayers. In case a plurality of such layers are employed which are arranged one above the other, care must be taken .that the number 'of turns per length unit is constant.- The medium interiorly of the coil may be made of a material of any desired permeability but having the property of being of even permeability at all places and of being invariable with the time. Most preferablya non-magnetizable substance is chosen, therefore a substance having a permeability u=1. If a greater sensitiveness is desired also a magnetizable material may be employed.

In Fig. 3 e is an iron body forming, for instance, a part of a dynamo-electric machine. For findi-n the magnetic tension between the two points 1 and 2 of the-iron,

now, the free ends of the instrument are laid against these places to .abut in such a way that the 'centerline of the coil at its ends will form an angle of 90 with the contact surface, and then the quantity of the magnetic tension may be measured. at the instrument m.

. 2 The line integral f .Q ds. is constant along two paths between the if the surface which is two paths is not permeated by the exciting ampere-turns. By this instrument, therefore, the magnetic tension in the iron body lpoints 1 and 2 in exact analo to the fact that in electrical circuits t e voltage may be measured by a voltmeter tapping two points of the circuit. If, however, the surface between this instrument and one path within the ironre be permeated by exciting amperemited by said between the two points will be measured turns, then, neglecting a constant factor, the

line integral of the magnetic field strength over the closed path from point 1 over the instrument to point 2 and in the iron 6 back to point 1 will be equal to the number of ampere-turns permeating the surface. The tension indicated bythe instrument will therefore not be equal to the magnetic tension to be determined between the two points 1 and 2 in the iron body, but differ from this by the number of exciting ampere-turns permeating the surface, said number being multiplied with the aforesaid constant factor. The number of exciting ampereturns being) easily obtainable by other measurements, y the aid of the instrument of my present invention the magnetic tension between the points 1 and 2 in the iron may thus readily be found. From this latter fact follows immediately, that with my present instrument it will also be possible to determine the number of ampere-turns of electrical circuits. For this purpose the instrument only needs tobe placed around the current-carrying windings of the electrical circuit and the ends of the instrument be united. In this case one will be enabled to determine the line integral of the mag netic field strength along a closed path surrounding the exciting ampere-turns.

Having thus. described my invention I claim as new and desire to secure by Letters Patent of the United States .1. The method of measuring the magnetic tension between two points of a magnetic circuit, which ,consists in variably exciting said magnetic circuit, branching said circuit scribing witnesses.

at said points, andmeasuring the electromotive force which is induced in a coil arranged in said branched circuit.

2. An instrument for measuring magnetic quantities consisting of a coil connected to an electrical measuring instrument and a core for said coil, the windings of said coil being evenly distributed over the entire length of said core, said core and said coil having their ends adapted to make close contact with the magnetic circuit to be tested.

3. An instrument for measuring magnetic quantities, consisting of a coil of even crosssection and evenly spaced turns throughout its length, said coil being adapted to make close contact at both ends with the material to be tested and means for measuring the magnetic flow inv said coil.

4. An instrument for measuring magnetic quantities, consisting of a flexible core of non-magnetic material, and having even cross-section, a winding thereon distributed uniformly over the entire length of said core, the end turns of said winding being shaped for making close contact with the material to be tested and an electrical measuring instrument connected to the ends of said winding.

In witness whereof I have hereunto set my signature in the presence of two sub- WALTER ROGOWSKI. Witnesses:

WOLDEMAR HAUPT, HENRY HAsrER. 

